ForeUI is a handy UI prototyping tool. It can rapidly create static or interactive, skinnable UI prototypes of your Web site or software. It features various UI themes (Wireframe, Windows, and Mac), interactive simulations that run in Web browsers, customized element creation, slide show and PDF exporting, and a rumple effect to suggest incompletion.

Ample SDK is a standards-based cross-browser JavaScript UI framework for building Rich Internet Applications running in a Web browser. It employs XML technologies (such as XUL, SVG, and HTML5) for UI layout, CSS for UI style, and JavaScript with DOM or jQuery APIs for application logic client-side. Ample SDK equalizes browsers and brings technology support to those missing any. The componentization model built into the core of the framework allows prototyping existing UI elements and creating new ones.

Fog-Framework is a high performance 2d vector graphics library that comes with platform abstraction classes and a platform-independent UI toolkit. Fog is a modern library that contains a multi-threaded architecture which efficiently utilizes your CPU and resources.

Mobiscroll is an easy to set-up and customize scroller/spinner JavaScript control. It renders date and time pickers, select controls, and various types of lists. It is suited for use on touch devices like smartphones and tablets.

Suil is a library for LV2 hosts intended to make using LV2 plugin UIs as
as simple as possible, including support for hosting a UI in any supported
toolkit in a host written in another supported toolkit.

PSArborTouch is a particle / spring physics engine optimized for 2D content layout and eye-catching visual effects. The goal is to build a high-quality physics based graph layout engine designed specifically for Mac OS X and iOS. The inspiration / structure comes from arbor, a dynamic and well structured JavaScript engine for the same purpose.
PSArborTouch is a graph visualization library built with GCD and Objective-C. Rather than trying to be an all-encompassing framework, it provides an efficient, force-directed layout algorithm plus abstractions for graph organization and screen refresh handling. It leaves the actual screen-drawing to you. This means you can use it with Quartz, Core Animation, or even positioned UIView's; whatever display approach is appropriate for your project and your performance needs. As a result, the code you write with it can be focused on the things that make your project unique (the graph data and your visual style) rather than spending time on the physics math that makes the layouts possible.

RedQueryBuilder fills the gap between a hand coded "quick search" and a full blown query language. A typical use is in an intranet Web application where experienced users need a quick ad-hoc way to find particular data. This means they don't have to use report frameworks or ask a techie. To use it in your app, you just need to drop in the JS, feed it the metadata for your database, then handle the change events to get the SQL and argument values.